To keep mice out, you need to do two things: physically block every way they can get in, and remove the food and shelter that makes your home worth entering. Deterrents and repellents fail when either of those two things is left undone. Sealing is the first step of the Seal-Trap-Clean sequence — the approach that resolves and prevents infestations permanently.
Key facts:
Mice fit through a hole the size of a dime. That means any gap around a pipe, crack in the foundation, or worn door seal is a potential entry point. Inspect the exterior of your home systematically:
What to seal with:
Seal the outside of the house first. Interior gaps (under sinks, around interior pipes) are secondary — mice that can't get into the structure don't reach them.
A sealed home with accessible food will still attract persistent attempts to get in. Remove the incentive:
Mice nest in clutter and use dense cover to move undetected. The closer that cover is to your house, the shorter their commute.
Garages are among the easiest entry points because the door seal is often imperfect and the space has clutter, warmth, and sometimes food. Check the bottom seal on your garage door — even a small gap is enough. Most hardware stores sell replacement garage door threshold seals that close the gap at ground level.
Inside the garage, store anything edible (birdseed, pet food, grass seed) in sealed metal or hard plastic containers. Mice treat an open bag of grass seed the same way they treat an open bag of cereal.
Mice enter cars through the engine bay, cabin air intake, and any opening in the undercarriage. They nest in air filter housings, inside seat cushions, and in the insulation under the hood — and they chew wiring while they're there.
Campers sitting unused are prime targets — warm, undisturbed, and often near fields or trees. Before storing a camper, plug every gap you can find with steel wool and foam. Check the underside, the water inlet, electrical access panels, and any pipe penetrations.
Inside, remove all food — even sealed packaged goods. Mice chew through Mylar and thin plastic. Place a few snap traps inside before closing it up for the season and check them when you return.
Peppermint oil may deter mice from a specific small area short-term. It doesn't replace sealing. A mouse that can enter freely and find food will ignore the smell.
Ultrasonic repellers are not supported by reliable evidence. Mice habituate to consistent sounds quickly. Don't substitute these for exclusion work.
Traps alone won't keep mice out — they only remove the ones already in. Trapping without sealing means you're playing catch-up indefinitely.
Even a well-sealed home should be checked periodically. Look for:
If you find these signs, you have a new entry point somewhere. Finding it quickly makes the problem much easier to contain. What mouse droppings look like →
If mice are already inside, exclusion alone won't solve it — you need to remove them first. How to get rid of mice →